Mobile operator Telefónica has announced a partnership with Line, the messaging service from Japan with over 300 million registered users. The deal is Line’s first with an overseas carrier and gives Telefónica exclusive access to the new Line for Firefox OS app, which is only available to the operator’s customers in Venezuela, Peru, Spain, Colombia, Uruguay, Brasil and Mexico.

In addition, Telefónica’s will pre-install Line on future Firefox OS handsets that it launches, it plans to make Line for Firefox OS available in more markets as it expands the availability of its phones to new countries.

Interestingly, the partnership also includes “significant marketing campaigns” by both companies in Latin America, which could be a big win for Line, since Telefónica has a customer of 320 million across 24 different markets.

Firefox OS is yet to make a dent on the global handset market but, with cheaper prices than high-end devices and an ‘open’ ecosystem, Telefónica is among a number of operators — including Telenor, Deutsche Telekom and TIM — that hope it will be a hit in emerging markets, where users spend less on devices and carrier subsidization is not common.

The deal makes a lot of sense for Line, which has placed great emphasis on growth in Latin America. Last year, Line US CEO Jeanie Han told us that the company shifted its focus on building its presence in the US to Latin America due to organic growth it had seen in the region.

“We originally thought we’d move in on the US, but then Latin America grew faster than we thought, and the timing there was more critical,” Han said.

Line isn’t alone in focusing on Latin America though. Rival WeChat, the chat app from China, recruited cult Argentine football star Lionel Messi to front its global campaign and boost its appeal in Latin America, while WhatsApp is also popular in that part of the world.

The deal with Telefónica is likely to boost Line’s visibility but the competition remains fierce and Firefox OS is a small part of the market — for now, at least. Now that it has its first international carrier deal in the bag, Line may well announce others, as it looks to replicate its success in Asia in other regions.